Thursday, November 20, 2008

60 Hertz vs. 120 Hertz

Many of you have probably already seen the new Televisions advertising 120Hz. Even though the number is double that of the previous televisions playing at 60Hz does it really make it twice as good?

A quick explanation of Hertz is the refresh rate at which the screen reconstructs the image per second or better known as frames per second (fps). So a television with 60 Hertz can display 60 different images per second. A television with 120 Hertz can display 120 different images per second.

The problem with such high framerate per second is that television broadcasts at only 30 frames per second. So with a 60Hz refresh rate it will simply repeat the image twice every second and with 120Hz it will repeat the image 4 times every second. So assuming you have to completely identical tv's, one playing at 120Hz and one playing at 60hz, you will not be able to tell a difference.

The difference between 120Hz and 60Hz comes when watching a movie. A movie is only shot at 24 frames per second compared to a video shot at 30 frame per second. A video has no problem being converted because it can simply be doubled, but a movie cannot just double because it would be 48fps and not 60fps. So they have to use a 3:2 pulldown. In a nutshell, 3:2 pulldown is an algorithm that displays some of the frames 3 times and some of them twice in order to map the film's 24 fps to 30 fps. With the 3:2 pulldown motion artifacts are introduced in fast moving scenes. With 120Hz though they can completely skip this element because 24fps goes evenly into 120hz 5 times. So essentially you are seeing each frame 5 times per second and it can completely phase out the 3:2 pulldown all together. For a more in depth article about the 3:2 pulldown visit: http://www.dvdfile.com